The present invention relates to a semiconductor device and a technique for manufacturing the same. Particularly, the present invention is concerned with a technique which is effectively applicable to a semiconductor device having terminals for external connection on a back surface (mounting surface) of a resin sealing member.
As semiconductor devices of the type in which a semiconductor chip is sealed with a resin sealing body, there have been proposed and practically used semiconductor devices of various package structures. For example, in Japanese Unexamined Patent Publication No. Hei 11(1999)-330343 there is disclosed a semiconductor device called QFN (Quad Flatpack Non-Leaded Package) type. The QFN type semiconductor device has a package structure wherein external connections (external terminals) formed on leads which are electrically connected to electrodes of a semiconductor chip are exposed from a back surface (mounting surface) of a resin sealing body. With this package structure, it is possible to attain the reduction of a planar size in comparison with a package structure, e.g., a semiconductor device called QFP (Quad Flatpack Package) type, wherein leads connected electrically with electrodes of a semiconductor chip are projected from side faces of a resin sealing body and are bent in a predetermined shape.
The QFN type semiconductor device is manufactured by an assembling process using a lead frame. For example, in the case of a package structure wherein a semiconductor chip is mounted on a die pad, the package structure is fabricated by mounting a semiconductor chip on a die pad (also called tab) which is supported by a frame body of a lead frame through suspension leads, then connecting electrodes on the semiconductor chip with leads electrically using bonding wires, the leads being supported by the frame body of the lead frame through tie bars (also called dam bars), thereafter sealing the semiconductor chip, leads, tie pad, suspension leads and bonding wires with a resin sealing body, and subsequently cutting off the leads, tie bars and suspension leads from the lead frame body. One ends of the bonding wires are connected to the electrodes on the semiconductor chip, while opposite ends thereof are connected to main surfaces of the leads which have the main surfaces and back surfaces opposite to the main surfaces. The main surfaces of the leads are covered with a resin sealing body and the back surfaces thereof are exposed from a back surface of the resin sealing body which has a main surface and the back surface (mounting surface) opposite to the main surface.
The resin sealing body used in the QFN type semiconductor device is formed by a transfer molding method suitable for mass production. According to the transfer molding method, the resin sealing body is formed by positioning a lead frame between an upper mold and a lower mold of a molding die so that a semiconductor chip, leads, die pad, suspension leads and bonding wires are positioned within a cavity (a resin sealing body forming portion), and thereafter injecting resin under pressure into the cavity of the molding die.
In the case of a package structure wherein external connections formed on leads are exposed from a back surface of a resin sealing body, it is fabricated by positioning a lead frame in such a manner that the external connections of the leads come into contact with a lower mold of a molding die and thereafter injecting resin under pressure into a cavity of the molding die. In this case, in the interior of the cavity, the lower mold and the external connections of the leads are not so closely in contact with each other, thus permitting easy entry of resin between the lower mold and the external connections, so that such an inconvenience as the external connections being covered with a thin film-like unnecessary resin (resin burr) is apt to occur.
To avoid the occurrence of such an inconvenience, in manufacturing a QFN type semiconductor device there is generally adopted a technique (hereinafter referred to as the “sheet molding technique”) wherein a resin sheet (resin film) is interposed between a lower mold of a molding die and a lead frame, then the lead frame is positioned relative to the molding die so that external connections of leads come into contact with the resin sheet, and thereafter resin is injected under pressure into a cavity of the molding die. According to this sheet molding technique, the resin sheet and the external connections of the leads are in highly close contact with each other in the interior of the cavity, whereby the occurrence of such an inconvenience as the external connections being covered with resin burr can be suppressed. The sheet molding technique is disclosed for example in Japanese Unexamined Patent Publication No. Hei 11(1999)-274195.